U.S. patent number 4,627,951 [Application Number 06/480,570] was granted by the patent office on 1986-12-09 for process for manufacturing composite products from lignocellulosic materials.
This patent grant is currently assigned to K. C. Shen Technology International Ltd.. Invention is credited to Kuo C. Shen.
United States Patent |
4,627,951 |
Shen |
December 9, 1986 |
Process for manufacturing composite products from lignocellulosic
materials
Abstract
A low cost process of making composite products from sugar
containing lignocellulosic materials, such as sugarcane bagasse and
stalks of sorghum, corn, sunflower, flax, and the like, utilizing
the residual sugars as bonding and bulking agent: Comminuted sugar
containing lignocellulosic material wholly composed of or partially
in combination with other lignocellulosic materials, in the absence
of adhesive binders or bonding agents, is molded at a temperature
of at least 180.degree. C., and a pressure and for a time
sufficient to compound the material into a composite product. The
free sugars in lignocellulosic materials act as a thermosetting
adhesive binder, and provide both bonding and bulking effect. The
composite thus produces possess great strength and excellent
dimensional stability. These results are obtained to the greatest
extent when the lignocellulosic materials contain higher proportion
of sugars.
Inventors: |
Shen; Kuo C. (Ottawa,
CA) |
Assignee: |
K. C. Shen Technology International
Ltd. (Ottawa, CA)
|
Family
ID: |
23908475 |
Appl.
No.: |
06/480,570 |
Filed: |
March 30, 1983 |
Current U.S.
Class: |
264/109;
264/123 |
Current CPC
Class: |
B27N
3/00 (20130101); C08L 97/02 (20130101); C08L
97/02 (20130101); C08L 5/00 (20130101); C08L
97/02 (20130101); C08L 2666/02 (20130101) |
Current International
Class: |
B27N
3/00 (20060101); C08L 97/02 (20060101); C08L
97/00 (20060101); B32B 005/16 () |
Field of
Search: |
;264/109,123 ;156/62.2
;106/200 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Ball; Michael
Attorney, Agent or Firm: Wray; R. W.
Claims
Having thus described my invention in preferred embodiment, I
claim:
1. A process for making waterproof composite products from
comminuted sugar containing lignocellulosic materials without the
addition of adhesive binders or chemical catalysts or high pressure
steam, which comprises the steps of separating the raw materials
into particles, fibres, strands, and flakes, drying the comminuted
raw materials, forming the previously dried raw materials into a
desired mat, pressing the mat in an open pressing step, and heating
the formed mat at a temperature of 180.degree. C. or higher and a
pressure and a time sufficient to consolidate said mat into a
molded article, while the adhesive bond is developed and thermoset
in situ, transforming and polymerizing sugars and water soluble
materials into an insoluble and infusible crosslinked substance as
bonding and bulking agent which is resistant to boiling water and
to acid hydrolysis, wherein the sugars and water soluble materials
contain lignocellulosic materials and are selected from sugar cane
stalks, sorghum stalks, corn stalks, and sun flower stalks.
2. The process of claim 1 wherein the sugars are free sugars,
carbohydrates or saccharides, which are water soluble, easily
extracted, and readily transformed, and thermoset with the
application of heat, into an insoluble and infusible substance
capable of bonding and bulking.
3. The process of claim 1 wherein the sugars and water soluble
materials occurring within the lignocellulosic materials are
chemically transformed and thermoset under an elevated temperature
of 180.degree. C. or higher into an insoluble and infusible
crosslinked polymeric substance, which provides both the bonding
and the bulking agent in the molded article.
4. The process of claim 1 wherein the hot molding and pressing
temperature is 220.degree. C. or higher.
5. The process of claim 1 wherein the sugars and water soluble
materials, which remain the finished composit products, are greatly
reduced through the chemical transformation and weight loss during
molding operation at an elevated temperature of 180.degree. C. or
higher.
6. The process of claim 1 wherein the sugar containing
lignocellulosic materials are comminuted and combined with other
lignocellulosic or non-lignocellulosic materials to produce
composite products.
7. The process of claim 1 wherein the sugars, water soluble
materials and pith are partially or not removed prior to
manufacturing.
8. The process of claim 1 wherein the sugar containing
lignocellulosic materials are comminuted to extremely fine
particles or fibers for the manufacture of composite products
having a strong bonding strength, an excellent dimensional
stability, and a tight, uniform, smooth and fine texture.
9. The process of claim 1 wherein the composite products are
building board, furniture board, reconsititute lumber, compressed
fire log, and molded articles with a water-proof bond which is
resistant to boiling water and acid hydrolysis.
Description
BACKGROUND OF THE INVENTION
This invention relates to the manufacture of composit products from
sugarcane bagasse, sorghum stalks, corn stalks, sunflower stalks,
flax stalks and other lignocellulosic materials, specifically of
non-woody plants containing sugars, carbohydrates, or saccharides,
which are water soluble and easily extracted.
More specifically, the invention relates to the manufacture of
composite products from sugar containing lignocellulosic materials
such as sugarcane bagasse, sorghum stalks, corn stalks, sunflower
stalks, flax stalks and the like, without the addition of adhesive
binders or bonding agents. This is accomplished by utilizing the
free sugars, carbohydrates or saccharides as both bonding and
bulking agents with the application of heat.
In the conventional manufacture of sugarcane bagasse panel
products, synthetic thermosetting resin binders such as
phenol-formaldehyde and urea-formaldehyde have been traditionally
used, with the more expensive phenol-formaldehyde being employed
for exterior grade products. Conventional resin binders account for
a large portion of the total material cost of composite products.
It is economically attractive to have composite products made
without the use of expensive resin binders. Furthermore, a
binderless manufacturing system simplifies the manufacturing
process, and reduces production cost by eliminating the blending
operation and equipment. Therefore, the desirability of using a
binderless process in the manufacture of composite products will be
readily appreciated from both economical and technological points
of view.
In the conventional manufacturing process of bagasse panel
products, the removal of pith and residual free sugars is essential
to good quality panel products. The pith, as compared to true
fibre, is a very short and thin-walled cell and contains a higher
portion of sugars but contributes no strength to the final product.
Because it is fluffy, the pith will absorb excessive resin binder
particularly when liquid resin is used. Pith also acts like a
sponge and soaks up water, swelling excessively if not removed from
the bagasse composite panel products. Also, bagasse normally
contains from 2 to 6 percent residual sugars, depending on the
variety of cane, its maturity, method of havesting and finally, the
efficiency of the sugar milling plant. The residual sugars in
bagasse, if not removed or minimized before processing, may cause
problems in board manufacturing and subsequently in service. Sugars
may not be chemically compatible with the conventional resin
binders used in bagasse board production and may interfere with
bonding, resulting in poor strength. If the residual sugars are not
chemically modified or consumed during hot pressing, they may start
to ferment when the bagasse board is exposed to humid conditions,
thus producing an unpleasant odor and culminating in chemical and
biological degradation. This would essentially shorten the useful
life of the bagasse board in service.
Consequently depithing and desugaring operations are necessary if
satisfactory products are expected to be manufactured from
sugarcane bagasse. These operations not only increase the
manufacturing cost but also complicate the process.
SUMMARY OF THE INVENTION
In contrast to the conventional process it has been found that
composite bagasse products such as building board, furniture board,
reconstituted lumber, and molded articles can be produced without
the use of resin binder, and the removal of pith and residual
sugars. Sugars, corbohydrates, or saccharides provide not only the
bonding agent but also the bulking element in the lignocellulosic
materials, resulting in a composite product with good strength
property and superb dimensional stability.
According to the present invention, the process essentially
requires a comminuted mass of bagasse or other lignocellulosic
materials containg high proportion of free sugars, particularly
from non-woody plants. The comminuted mass was first dried to a low
moisture content, preferably in 2-8 percent based on oven dry
weight. This mass may be wholly composed of or partially combined
with other lignocellulosic or non-lignocellulosic materials. The
mass is molded without any added resin binders at a temperature of
at least 180.degree. C. and at a pressure sufficient to compound
the material into a molded product, for a sufficient period of time
to develop and thermoset the bond in situ, transforming the
residual sugars to an insoluble and infusible polymeric substance
which is highly resistant to boiling water and acid hydrolysis.
The comminution of raw materials is especially useful, because
individual particles, flakes or strands facilitate and improve the
forming and molding operation. Furthermore comminution also reduces
and minimizes the presence of epidermal material from the stem of
plants. The thin exterior layer of epidermix, which normally
consists of cuticle material, is impervious to water and to
adhesive bonding. In a binderless system, finer particles usually
produces better products, mainly because of uniform and close
compact between individual particles, resulting in a strong bond, a
tight and smooth texture. On the contrary, the conventional process
is economically not able to use finer particles, because finer
particles require increased amount of expensive synthetic resin
binder. The present invention prefers to use extremely fine
particles when combined with other non-sugar containg
lignocellulosic materials in manufacture composite products.
Essentially the fine particles act as a pawdered resin binder in
the conventional manufacturing process.
DESCRIPTION OF PREFERRED EMBODIMENT
The favorable effect of the use of sugarcane bagasse and other
sugar containing lignocellulosic materials of non-woody plants in
particular, may be ascribed to the sugars and water soluble
materials occurring within, which will flux during the hot molding
operation and will polymerize and bond in-situ the lignocellulosic
material together. In addition, the sugars and water soluble
materials, which permeated within cell wall of lignocellulosic
tissues will also be transformed and thermoset to a crosslinked
rigid substance, acting as a bulking agent throughout the entire
molded article. Thus, the molded articles display an excellent
strength property, dimensional stability and resistance to boiling
water and to acid hydrolysis. These results are obtained to the
greatest extent when the lignocellulosic materials contain a high
proportion of sugars and water soluble materials.
The chemical reactions involved in the bonding system in the
present invention have been fully elucidated. It is well known that
sugar is degraded to compounds of small molecule weight by both
acid and alkalis, with the loss of water from the sugar molecule.
If a weak acid, or even pure water at a temperature of
130.degree.-170.degree. C. and under pressure is reacted with
sugar, about 20 percent of hydroxymethyl-furfural is produced.
Other intermediates and furfural derivatives may also be produced
from carbohydrates under similar conditions. These derivatives are
very reactive which can further polymerize and transform to produce
insoluble and infusible crosslinked substances at elevated
temperature. Thus the thermoset bond so produced is highly
resistant to boiling water and to acid hydrolysis.
It is believed that all or some of the above mentioned reactions
may be involved in the bonding formation process of the present
invention. It is further believed that chemical transformation of
sugars and water soluble materials at elevated temperature is an
irreversible chemical and physical change and is essential to the
present invention. It is assumed that the polymerized bonding and
bulking substance of the present invention contains a furan
dehydration product of the carbohydrate which consists essentially
of hydroxymethyl-furfural.
It has been found that the physical and mechanical properties of
sugarcane bagasse board produced by the present invention are at
least comparable to or better than the properties of conventional
bagasse boards produced by hitherto use of expensive synthetic
resin binders.
Embodiment of the invention will be described and illustrated in
detail in the following examples.
EXAMPLE 1
Dried sugarcane bagasse containing 3.8 percent moisture content was
obtained from a conventional sugar milling factory. It contained
7.2 percent by weight of water soluble materials from which 4.7
percent of reducing sugars (as glucose), determined by Swedish
Cellulose Industry method CCA-11 was found. Futher
experimentatation indicated the bagasse contained about 70 percent
true fibre and 30 percent pith by weight.
The bagasse was hammermilled to produce two fractions of particles.
Particles passing a 16 mesh tyler screen were used for the face
layer and particles larger than 16 mesh were used as core material
for a 3-layer mat. The face and core ratio by oven dry weight was 1
to 1. From this mat, a board 500.times.500.times.11.1 mm, was hot
pressed for 12 minutes to a specific gravity of 0.72 at a
temperature of 235.degree. C. and a pressure of 2.8 MPa. During the
hot-passing, it was noted that a certain amount of material other
then the moisture was evaporated in form of steam and various
fumes. The weight loss of the mat amounted to 8.4 percent, far more
than the original mat miosture content of 3.8 percent. The extra
weight loss indicated the rigorous chemical reaction under elevated
temperatures. Final analysis confirmed that only 0.7 percent of
reducing sugar was found remaining in the finished board. It was
far less than that found in a commercial bagasse board.
Bending strength tests showed a dry MOR (modules of repture) of
16.3 Mpa and a dry MOE (modules of elasticity) of 3.8 Gpa. The wet
MOR was 8.6 Mpa. The wet bending strength was obtained by immersing
the specimens in boiling water for two hours and then testing them
wet and cold. The boil test is required by Can-3-0188-2M78 standard
for exterior grade poplar waferboard. The Canadian minimum
standards for dry and wet MOR are 14 and 7 Mpa respectively. In
summary the bagasse board met all the Canadian standards for wood
composit panel specified for exterior application.
EXAMPLE 2
Sugarcane rinds were produced by a sugarcane separator machine
which separates the inner sugar containing soft pith from the outer
hard layer, or rind of the sugarcane stalk. The rind bagasse
contained 28.6 percent water soluble materials and 17.3 percent
reducing sugars because sugars were not extracted from it.
The rind bagasse was shredded to strands of 1.5 to 3.2 mm in both
width and thickness, and containing about 5 percent moisure.
Strands ranged in lengths from 15 to 300 mm and were oriented in
one direction to be molded into a composite lumber having a
dimension of 38.times.50.times.2650 mm and a specific gravity of
0.65. The molding temperature was 225.degree. C. at a pressure of
3.4 Mpa for 30 minutes. Bending strength tests showed a dry MOR of
31.6 Mpa and a wet MOR of 18.6 Mpa.
EXAMPLE 3
Fresh sugarcane rinds produced from a sugarcane separator machine
were treated to remove sugars by boiling them in water for
different lengths of time. Three batches of rind were subjected to
a 5, 10 and 30 minute boiling period respectively, and a fourth
batch was not boiled but included in the experiment as a control.
After boiling, the rinds were dried to an 8 percent moisure content
and than hammer milled into the factions of .+-.20 mesh tyler
screen. Chemical analysis indicated that the resulting residual
sugars are inversely proportional to the increase in the boiling
period. It also revealed a close linear relationship between water
soluble materials and reducing sugars. The following Table 1 lists
the results of the boiling treatment.
TABLE 1 ______________________________________ SUGAR CONTENT OF 4
BATCHES OF RIND TREATED BY BOILING IN WATER SOLUBLE REDUCING BATCH
TREATMENT EXTRACTED SUGAR NO. (BOILING) (%)* (%)*
______________________________________ #1 NONE 24.4 15.2 #2 5 MIN
16.0 11.2 #3 10 MIN 12.3 10.2 #4 30 MIN 5.4 3.7
______________________________________ *Content in terms of oven
dry weight of rind fibre.
Each batch of rind furnish was used to make six boards of
500.times.500.times.11.1 mm and a specific gravity of about 0.70,
using three different press temperatures (180.degree., 210.degree.
and 240.degree. C.) two different press times (10, and 20 minutes)
and a closing pressure of 3.4 Mpa. The moisture content of face
layer furnish (-20 mesh) was about 9.0 percent and the core furnish
(+20 mesh) was 3.0 percent. The face and core ratio by oven dry
weight of the mat was 1 to 1. Test results on 48 boards, are listed
in the following Table 2.
TABLE 2
__________________________________________________________________________
PROPERTIES OF SUGAR CANE RIND BOARDS (11.1 mm) PRESS CONDITION
SPECIFIC MOE MOR(MPa) IB SWELL SPRINGBACK RIND BATCH Temp
(.degree.C.) Time (M) GRAVITY (GPa) Dry Wet (kPa) (%) (%)
__________________________________________________________________________
No. 1 Control 180 10 0.72 5.01 23.0 5.2 686 23 10.8 (15.2% Reducing
20 0.74 5.12 22.3 7.7 749 18 9.2 Sugar) 210 10 0.72 5.06 23.2 10.4
658 13 7.1 20 0.75 5.20 23.3 11.5 714 9 3.8 240 10 0.74 4.85 20.7
11.0 679 11 1.6 20 0.75 5.24 23.5 14.5 735 7 0.7 No. 2 5 min. 180
10 0.73 4.91 17.3 3.0 644 27 13.3 Boil 20 0.75 5.00 19.1 5.4 623 21
11.0 (11.2% Reducing 210 10 0.73 4.85 19.0 8.3 630 19 8.5 Sugar) 20
0.76 4.81 18.6 9.1 679 16 3.1 240 10 0.75 5.01 19.5 10.8 630 16 3.8
20 0.75 5.05 19.2 11.4 602 15 2.7 No. 3 10 min 180 10 0.70 4.75
18.1 1.9 574 29 16.4 Boil 20 0.72 4.72 18.4 3.8 616 25 13.7 (10.2%
Reducing 210 10 0.72 4.59 17.6 6.2 630 24 14.5 Sugar) 20 0.73 4.76
18.8 7.4 637 19 11.6 240 10 0.73 4.66 18.7 8.5 602 18 11.8 20 0.75
4.91 18.3 9.2 623 16 9.2 No. 4 30 min. 180 10 0.70 3.03 15.0 0.7
266 44 23.5 Boil 20 0.72 3.23 16.6 2.1 297 38 19.7 (3.7% Reducing
210 10 0.73 3.00 16.4 4.5 288 36 18.4 Sugar) 20 0.73 2.88 16.8 5.1
302 25 16.2 240 10 0.74 3.33 15.7 6.4 416 29 17.1 20 0.75 3.05 16.0
7.3 430 22 15.3
__________________________________________________________________________
CAN3-0188.2M78 (Waferboard) sets forth the minimum requirements for
MOE: 2.70 GPa, MOR: 14.0 and 7.0 MPa respectively for dry and wet,
and IB: 280 kPa.
It was evident from these test results as indicated in Table 2,
that board properties improved as sugar content of rind increased.
Higher press temperature and longer press time also enhanced board
quality. The rind furnish board had a tight, smooth surface and
dark brownish colour mainly due to the extremely fine particles,
and high sugar and moisture content in facelayer of the mat. The
dimensional stability of the rind bagasse board, particularly of
those made with higher sugar content and rigorous pressing, was
excellent compared to the products of the conventional process.
This resulted from the bonding and the bulking effect of
polymerized sugars.
EXAMPLE 4
This example illustrates sugarcane bagasse in combination with
other lignocellulosic materials to form a mixed composite
product.
Sugarcane rind bagasse which contained about 19 percent reducing
sugars was hammer milled to pass through a 20 mesh tyler screen.
These rind bagasse splinters were mixed with poplar wood splinters
of similar size at a ratio of 70:30 by weight. From the mixture was
formed a mat that was hot-pressed at 235.degree. C. with 2.8 Mpa
pressure for 10 minutes, producing a 500.times.500.times.11.1 mm
board with a specific gravity of 0.72. Static bending tests showed
a dry MOR of 18.2 Mpa and a wet MOR of 8.1 Mpa. The internal
bonding test gave a tension perpendicular strength of 390 kPa. All
the testing values surpassed the minimum requirements by CAN
3-0188-2M78.
EXAMPLE 5
This example illustrates that similar results can be produced with
other sugar containing lignocellulosic materials.
Sweet sorghum stalks which contained about 18 percent reducing
sugars were dried to 3 percent moisure content and hammer milled to
pass through a 20 mesh tyler screen. A board
(500.times.500.times.11.1 mm and 0.75 specific gravity) was made
with this furnish under the similar press conditions outlined in
Example 4. Test results showed a dry MOR of 18.5 Mpa, wet MOR of
9.2 Mpa, and an internal bond strength of 480 kPa.
Corn stalks which contained about 12% soluble materials or about 7%
reducing sugars were dried to 3% moisture content and hammer milled
to pass through a 20 mesh tyler screen. A board
(500.times.500.times.11.1 mm and 0.82 specific gravity) was made
with this furnish under the similar press condition outlined in
Example 4. Test result showed a dry MOR of 14.3 Mpa wet MOR of 7.4
Mpa, and an internal bonding strength of 320 Kpa.
* * * * *